1. Technical Field
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device with a feedback circuit part to compensate for ripple voltages.
2. Related Art
Recently, reduced weight lightening and a thin shape of display devices have been required consistent with reduced weight and thin shape of personal computers, televisions, etc., and flat panel displays such as liquid crystal display devices (as opposed to cathode ray tube (CRT) device) are continuously being developed according to such a demand.
The liquid crystal display device is a display device for obtaining a desired image signal by impressing an electric field on liquid crystals having an anisotropic dielectric constant, and injected between two substrates, and controlling the intensity of the electric field, thereby controlling the amount of light transmitted onto the substrates from an external light source (a backlight).
The liquid crystal display device is typical of display devices in simply portable flat panel displays, and a thin film transistor-liquid crystal display device (TFT-LCD) in which a thin film transistor is used as a switching device is mainly used in the liquid crystal display device.
Generally, the liquid crystal display device comprises a liquid crystal panel comprising liquid crystals injected onto upper and lower substrates and between the upper and lower substrates, a driving circuit for driving the liquid crystal panel, and a backlight for providing the liquid crystals with white light. The liquid crystal display device is divided into two types of liquid crystal displays, those employing an R, G and B color filter and those employing a color field sequential arrangement for displaying color images.
The color filter driving type liquid crystal display is constructed in such a manner that one pixel is divided into R, G and B sub-pixels, and R, G and B color filters are aligned on each R, G and B sub-pixels so as to display a color shape by transmitting light from one backlight to the R, G and B color filters through liquid crystals.
The color field sequential driving type liquid crystal display obtains a full color image by lighting independent light sources of respective R, G and B colors sequentially and periodically, and by applying corresponding color signals to the respective pixels while being synchronized with lighting cycles of the light sources. Namely, the color field sequential driving type liquid crystal display is constructed in such a manner that R, G and B backlights are aligned in one pixel that is not divided into R, G and B sub-pixels so as to display a color shape using persistence of vision of eyes by sequentially displaying light of R, G and B colors that are the three primary colors on one pixel through liquid crystals from R, G and B backlights in a time-sharing manner.
Therefore, the color field sequential driving type liquid crystal display achieves very large scale integration (VLSI) since only one third of the number of pixels are required in the color field sequential driving type liquid crystal while maintaining the same resolution as in the color filter type liquid crystal display, and the color field sequential driving type liquid crystal display has the advantage of being able to realize the same color reproducibility and high speed moving images as color televisions are able to realize.
The color field sequential driving type liquid crystal display is driven with one frame being divided into three sub-frames since the color field sequential driving type liquid crystal display displays a color shape by synthesizing lights of R, G and B primary colors. In addition, driving times of R, G and B backlights for one pixel are varied differently from those in a color filter type liquid crystal display in which lights are sequentially scanned from an upper part of a screen to a lower part of the screen.
Furthermore, one frame is divided into an R sub-frame for displaying an R color, a G sub-frame for displaying a G color, and a B sub-frame for displaying a B color. That is, the R sub-frame displays the R color by driving an R backlight, the G sub-frame displays the G color by driving a G backlight, and the B sub-frame displays the B color by driving a B backlight. Therefore, one frame is divided into respective sub-frames for displaying R, G and B colors and has three sub-frame sections sequentially emitted through R, G and B backlights.
The color field sequential driving type liquid crystal display has an advantage in that it enables about three times the resolution to be realized on the same sized panel compared with the color filter driving type liquid crystal display, and its light efficiency is increased since color filters are not used. On the other hand, the color field sequential driving type liquid crystal display needs high speed movement characteristics that require a driving frequency as high as six or more times that of the color filter driving type liquid crystal display since the color field sequential driving type liquid crystal display is driven with one frame being divided into three sub-frames.
Since liquid crystals are degraded due to their characteristics when they are continuously driven by voltages of the same polarity, the liquid crystals should be driven by voltages of opposite polarities. Therefore, if a voltage of positive polarity is impressed on an arbitrary one pixel, a voltage of negative polarity should be impressed on the pixel in the next frame so as to drive the pixel.
Conventional liquid crystal displays are characterized by the following problems, which are overcome by the present invention.
Such liquid crystal display devices generate black points, caused by blackening phenomena, and blinking pixels, so that the image quality of the liquid crystal display panel deteriorates, and the life of the liquid crystal display panel is shortened due to ripple voltages generated by a common electrode of a common substrate.